Annular catalyst carrier container for use in a tubular reactor

ABSTRACT

In a catalyst carrier for insertion in a reactor tube of a tubular reactor, the catalyst carrier includes a container for holding catalyst in use. The container has a bottom surface closing the container, and a top surface. A carrier outer wall extends from the bottom surface to the top surface. A seal extends from the container by a distance which extends beyond the carrier outer wall. The carrier outer wall has apertures located below the seal.

The present invention relates to a catalyst carrier for use in a tubularreactor and to processes carried out using the catalyst carrier. Moreparticularly, it relates to a catalyst carrier for use in a tubularreactor in which an exothermic or an endothermic reaction is to becarried out. Still more particularly, it relates to a catalyst carrierfor use in a reactor for carrying out an exothermic or endothermicreaction comprising a plurality of said catalyst carriers.

Conventional, so-called fixed bed tubular, reactors comprise a reactorshell containing a plurality of tubes, which are usually cylindrical,and which are usually filled with catalyst particles. In use, a heattransfer medium flows through the shell of the reactor outside thesetubes and thereby adjusts the temperature of the catalyst in the tubesby heat exchange across the tube wall. Thus, where the reaction is anexothermic reaction, the heat transfer medium will allow heat to beremoved from the catalyst and where the reaction is an endothermicreaction, the heat transfer medium will provide heat to the catalyst.Examples of heat transfer mediums include cooling water, boiler feedwater and heat transfer oils such as that sold under the trade markDowtherm by The Dow Chemical Company. Alternatively the heat transferfluid is in the form of a molten salt mixture. During operation, gas,liquid, or both gas and liquid reactants flow through the tubes over thecatalyst particles such that the desired reaction takes place.

For some reactions, the heat effects of the reaction are moderate suchthat they are either not problematic or they can be readily managed. Insome cases, the heat effects are sufficiently small that large-diametertubes may be used. This has the benefit that there is a large volume ofcatalyst within the tube. However, for more exothermic reactions it isnecessary that there is efficient heat transfer via the tube wall to theheat transfer medium to enable the conditions within the reactor to becontrolled. To achieve the desired efficiency, the surface area of thetube wall per unit length has to be maximised. This is achieved byinstalling a greater number of smaller diameter tubes. The use of thismultiplicity of tubes increases the cost and complexity of the reactor.

Tubular reactors in which moderate to highly exothermic reactions takeplace are in many cases, heat transfer limited. One disadvantage of thisis that the benefits of more active catalysts are difficult to realisesince the increased productivity achievable with these catalystsgenerates increased amounts of heat which must be removed at a rate thatmaintains a stable operating temperature to avoid detrimental effectsoccurring such as side reactions taking place, damage to the catalystsuch as by sintering of the catalytic active sites, and, in the worstcase, thermal runaway. Where the reaction is a moderate to highlyexothermic reaction, various problems can arise with this increasedheating and in some systems the heat can be such that the catalyst canfail and even damage to the tube wall can occur.

Where the reaction is a moderate to highly exothermic reaction, problemscan arise with increased heating and in some systems damage to the tubewall can occur, for example uneven heating can result in temperature hotspots on the tube wall.

Conventional reactors have a number of drawbacks that make them lessthan ideal. One problem that is noted for these reactors is that inorder to extract the heat of reaction effectively the tubes have to berelatively small in diameter to ensure that the central region of thetube remains cool enough to avoid the problems detailed above occurring.

Similar, albeit converse problems, will be noted where the reaction isan endothermic reaction. In order for the heat to be provided such thatthe catalyst can continue to operate in the optimum manner, the tubeshave to be relatively small in diameter to ensure that the centralregion of the tube is heated sufficiently.

In some reactions, the size restriction means that the tubes are only ofthe order of about 15 to 40 mm internal diameter. The small size of thetube means that, in order to accommodate the required volume of catalystin the reactor, a large number of tubes have to be used. However, thisincreased number of tubes increases the weight of the reactor and sincethere is generally a maximum size of reactor which can be shipped interms of dimensions and weight, the productivity of the reactor islimited.

A second problem is that the catalyst particles have to be a certainsize, shape and strength so as not to cause an undue pressure drop foran appropriate tube length and in general this leads to the use oflarger catalyst particles. However, the use of larger particles may beproblematic where the reaction is mass, heat, or both mass and heattransfer limited, or both. Whilst some of these problems may bealleviated by ensuring that the active sites are only present near thesurface of the catalyst particle, this can limit the productivity thatcan be achieved since the available active sites have to be workedharder to deliver a reasonable overall productivity. Whilst this maygive reasonable productivity at a given time, it can reduce the life ofthe catalyst.

A further problem is that there is a limitation on the amount of heatthat can be removed per unit surface area of the tube wall and this putsa limit on the amount of generated heat that can be tolerated per unitvolume of catalyst contained within the tube.

In WO2011/048361 an alternative approach to packing catalyst in tubes issuggested in which a catalyst carrier device is configured to sit withinthe reactor tube. This arrangement optimises heat transfer at the tubewall such that larger tubes and larger volumes of smaller catalystparticles can be used. This arrangement allows the reactor to beoperated at high productivity and with an acceptable pressure drop evenwhere the reaction is highly exothermic.

The catalyst carrier described in WO 2011/048361 comprises:

-   -   an annular container for holding catalyst in use, said container        having a perforated inner wall defining a tube, a perforated        outer wall, a top surface closing the annular container and a        bottom surface closing the annular container;    -   a surface closing the bottom of said tube formed by the inner        wall of the annular container;    -   a skirt extending upwardly from the perforated outer wall of the        annular container from a position at or near the bottom surface        of said container to a position below the location of a seal;    -   and a seal located at or near the top surface and extending from        the container by a distance which extends beyond an outer        surface of the skirt.

Whilst these carriers offer substantial advantages over conventionalpacked tubes, they may suffer from some disadvantages and drawbacks forsome applications. A particular problem may be attributed to the factthat the load bearing components of the carrier are the perforated innerand outer walls. When a plurality of filled carriers is packed in atube, the weight of each packed carrier is supported by the perforatedinner and outer walls of the carriers below. Since in some arrangementsthere may be 80 or even more filled catalyst carriers in a tube theweight carried by the carriers located towards the base of the tube canbe substantial.

This means that the perforated inner and outer walls of the container,the primary function of which is to retain the catalyst particles, haveto be fabricated from materials which are stiff enough and strong enoughnot to buckle or otherwise distort under the load of the filled catalystcarriers located above it in the tube. This is especially importantduring the insertion and removal of the containers from the tubes. Thiswill generally mean that thicker material will have to be used. The needto use thicker material will increase the manufacturing cost of thecarrier.

Further, the use of thicker material to manufacture the perforated innerand outer walls will increase the pressure drop of the gas flowingthrough the thicker perforated walls. This will generally result in anincreased operating cost since in most cases the gas must be compressedto overcome the pressure drop. Having to compress the gas will increasethe energy requirements of the process.

A still further drawback is that where the perforated inner and outerwalls are fabricated from thicker material they take up more volumewithin the carrier. Whilst this may not have a significant effect wherelarger carriers are used, such as those having a diameter of about 3inches (7.62 cm) or more, for smaller containers, such as those having adiameter of about 1 (2.54 cm) to about 2 inches (5.08 cm), if a materialhaving a thickness of about 2 mm is used for the manufacture of theperforated walls, 8 mm of the available internal diameter will be takenup with the perforated walls. This then limits the amount of catalystwhich can be located within the carrier and hence will limit the amountof reaction that can be achieved.

In addition, if there is any flex in a radial direction in the innerperforated wall, the outer perforated wall or both perforated walls,then additional compressive loads will be imposed on the catalystparticles. It is therefore necessary to use a catalyst with a crushstrength which is high enough to avoid the catalyst being crushed by theweight of the filled carriers located above it in the reactor tube.Whilst the crush strength required will be less than that required withconventional filled tubes, it would still be desirable to provide acatalyst carrier that is configured such that the compressive strengthof the catalyst does not have to be considered when selecting thecatalyst.

An alternative catalyst carrier for use where the catalyst is a monolithcatalyst is disclosed in WO2012/136971. In this arrangement, thecatalyst carrier comprises:

-   -   a container for holding a monolith catalyst in use, said        container having a bottom surface closing the container and a        skirt extending upwardly from the bottom surface of said        container to a position below the location of a seal and spaced        therefrom, said skirt being positioned such that there is a        space between an outer surface of the monolith catalyst and the        skirt; and    -   a seal located at or near a top surface of the monolith catalyst        and extending from the monolith catalyst by a distance which        extends beyond an outer surface of the skirt.

Thus in this arrangement there is no perforated inner or outer wall andthe weight of the stack of carriers and catalysts must be borne by themonolith catalyst itself. This places additional constraints on thecomposition of the monolith catalyst which can be used. If the thicknessof the walls within the monolith has to be increased to provide thenecessary strength, the voidage within the monolith will be reduced.This will decrease the free area for gas flow and an increase inpressure drop may result.

A further problem with the catalyst carriers for both particulate andmonolith catalysts is that as the upwardly extending skirt from thebottom surface of the container is only connected to the carrier at ornear the bottom surface, it may, depending on its thickness, flex in onedirection and no longer be concentric within the reactor tube. If theskirt is distorted such that it becomes ovoid at the top then the flowof reactants will be preferentially down the larger gap which willresult in poorer heat transfer.

Whilst the skirt could be fabricated from thicker material to minimisethe risk of distortion, this will increase production costs and increasethe weight of the carrier. In addition, the carrier will be moredifficult to fabricate since it is harder to roll thicker material intoa perfect cylinder.

It is therefore desirable to provide an improved catalyst carrier inwhich one or more of the above-mentioned problems can be addressed andpreferably overcome.

The present invention solves the above problems by the provision of acatalyst carrier in which the upwardly extending skirt of the prior artis extended so that it joins the surface closing the bottom of the tubeand the top surface. Thus the skirt of the prior art carriers becomesthe outer wall of the carrier. Apertures will be provided towards thetop of the outer wall to allow the fluid flow. Thus in the catalystcarriers of the present invention, the primary load bearing section ofthe catalyst carrier is the outer wall. In some arrangements, the loadwill be carried by the top surface, the base and the outer wall. By thismeans the problems noted with the prior art arrangements may beaddressed and preferably are obviated.

Thus according to the present invention there is provided a catalystcarrier for insertion in a reactor tube of a tubular reactor, saidcatalyst carrier comprising:

-   -   a container for holding catalyst in use, said container having a        bottom surface closing the container, and a top surface;    -   a carrier outer wall extending from the bottom surface of said        container to the top surface;    -   a seal extending from the container by a distance which extends        beyond the carrier outer wall;    -   said carrier outer wall having apertures located below the seal.

In one arrangement, which is particularly suitable where the catalyst isa particulate or a foamed catalyst, the catalyst carrier comprises:

-   -   an annular container for holding catalyst in use, said container        having a perforated inner container wall defining an inner        channel, a perforated outer container wall, a top surface        closing the annular container and a bottom surface closing the        annular container;    -   a surface closing the bottom of said inner channel formed by the        inner container wall of the annular container.

For the avoidance of doubt, any discussion of orientation, for exampleterms such as upwardly, below, lower, and the like have, for ease ofreference been discussed with regard to the orientation of the catalystcarrier as illustrated in the accompanying drawings. However, thecatalyst carrier of the present invention could also be used in analternative orientation for example horizontally. Thus the terms shouldbe constructed accordingly.

The catalyst carrier will generally be sized such that it is of asmaller dimension than the internal dimension of the reactor tube intowhich it is to be placed in use. The seal will be sized such that itinteracts with the inner wall of the reactor tube when the catalystcarrier of the present invention is in position within the reactor tube.Parameters such as carrier length and diameter will be selected toaccommodate different reactions and configurations.

In use in a vertical reactor with downflow, reactant(s) flow downwardlythrough the reactor tube and thus first contact the upper surface of thecatalyst carrier. Since the seal blocks the passage of the reactant(s)around the side of the carrier, the top surface thereof directs theminto the inner channel defined by the inner container wall. Thereactant(s) then enters the annular container through the perforatedinner container wall and then passes radially through the catalyst bedtowards the perforated outer container wall. During the passage from theinner container wall to the outer container wall, the reactant(s)contact the catalyst and reaction occurs. Unreacted reactant and productthen flow out of the container through the perforated outer containerwall. The carrier outer wall then directs reactant and product upwardlybetween the inner surface of the carrier outer wall and the perforatedouter container wall of the annular container until they reach theapertures in the carrier outer wall. They are then directed through theapertures located in the carrier outer wall and flow downwardly betweenthe outer surface of the carrier outer wall and the inner surface of thereactor tube where heat transfer takes place.

The top surface of the container may be of any suitable size andconfiguration. In the arrangement where the carrier comprises anperforated inner and outer container wall, the top surface will at leastextend outwardly from the perforated outer container wall and willconnect with the carrier outer wall. In one alternative arrangement thetop surface may extend from the perforated inner container wall to thecarrier outer wall. It will be understood that the top surface may be anannulus which extends from a point between the location of theperforated inner container wall and the perforated outer container wallto the carrier outer wall.

In one arrangement, a cap may close the inner channel formed by theperforated inner container wall. This cap will include one or moreapertures to allow for fluid flow into the inner channel.

The size of the perforations in the inner container wall and the outercontainer wall will be selected such as to allow uniform flow ofreactant(s) and product(s) through the catalyst while maintaining thecatalyst within the container. It will therefore be understood thattheir size will depend on the size of the catalyst particles being used.In an alternative arrangement the perforations may be sized such thatthey are larger but have a filter mesh covering the perforations toensure catalyst is maintained within the annular container. This enableslarger perforations to be used which will facilitate the free movementof reactants without a significant loss of pressure.

It will be understood that the perforations may be of any suitableconfiguration. Indeed where a wall is described as perforated all thatis required is that there is means to allow the reactants and productsto pass through the walls. These may be small apertures of anyconfiguration, they may be slots, they may be formed by a wire screen orby any other means of creating a porous or permeable surface.

Although the top surface closing the container will generally be locatedat the upper edge of the inner container wall and/or the outer containerwall, it may be desirable to locate the top surface below the upper edgesuch that a portion of the upper edge of the carrier outer wall extendsabove the top surface. Similarly, the bottom surface may be located atthe lower edge of the inner container wall and/or the outer containerwall or it may be desirable to locate the bottom surface such that it isabove the bottom edge of the outer container wall such that it extendsbelow the bottom surface. Where the carrier outer wall extends above thetop and/or the bottom surface, this may facilitate the stacking ofcontainers against others when in use. Additionally or alternatively,this configuration may be configured to facilitate connecting thecatalyst carrier to adjacent catalyst carriers in use.

The bottom surface of the annular container and the surface closing thebottom of the inner channel may be formed as a single unit or they maybe two separate pieces connected together. The bottom surface of theannular container and the surface closing the bottom of the innerchannel may be coplanar but in one arrangement, they are in differentplanes. In one arrangement, the surface closing the bottom of the innerchannel is in a lower plane than the bottom surface of the annularcontainer. This may serve to assist in the location of one catalystcarrier onto a catalyst carrier arranged below it when a plurality ofcatalyst carriers are to be used. It will be understood that in analternative arrangement, the surface closing the bottom of the innerchannel may be in a higher plane that the bottom surface of the annularcontainer. This may assist in the location of one carrier onto a carrierarranged below it.

Whilst the bottom surface will generally be solid, it may include one ormore drain holes. Where one or more drain holes are present, they may becovered by a filter mesh. Similarly a drain hole, optionally coveredwith a filter mesh may be present in the surface closing the innerchannel. Where the carrier is to be used in a non-vertical orientation,the drain hole, where present will be located in an alternative positioni.e. one that is the lowest point in the catalyst carrier when in use.

One or more spacer means may extend downwardly from the bottom surfaceof the catalyst carrier. The, or each, spacer means may be formed asseparate components or they may be formed by depressions in the bottomsurface. Where these spacer means are present they assist in providing aclear path for the reactants and products flowing between the bottomsurface of the first carrier and the top surface of a second lowercarrier in use. The spacer may be of the order of about 4 mm or about 5mm to about 6 mm to about 25 mm deep. Alternatively, or additionally,spacer means may be present on the top surface.

The top surface may include on its upper surface means to locate thecatalyst carrier against a catalyst carrier stacked above the carrier inuse. The means to locate the carrier may be of any suitable arrangement.In one arrangement it comprises an upstanding collar having apertures orspaces therein to allow for the ingress of reactants.

In an alternative arrangement, which is particularly suitable for amonolith catalyst, the container is configured for holding a monolithcatalyst in use.

In one arrangement, the monolith catalyst is a solid, in that there issubstantially no space within the body of the monolith that is notoccupied by catalyst. When the monolith is in use in a vertical reactorwith downflow, the reactant(s) flow downwardly through the reactor tube,the reactant(s) first contacts the upper face of the monolith catalystand flows therethrough in a direction parallel to the axis of thecatalyst carrier. The seal of the container prevents the reactant(s)from flowing around the monolith and assists the direction of thereactants into the catalyst. Reaction will then occur within themonolith catalyst. The product will then also flow down through themonolith in a direction parallel to the axis of the catalyst carrier.

In the arrangement where the catalyst is a monolith catalyst, the topsurface will at least extend outwardly from the monolith catalyst andwill connect with the carrier outer wall. It will be understood that thetop surface may be an annulus which extends over at least a portion ofthe monolith catalyst to the carrier outer wall

Once the reactant(s) and product reach the bottom surface of thecontainer they are directed towards the carrier outer wall. Tofacilitate this flow, feet may be provided within the container on theupper face of the bottom surface such that, in use, the catalystmonolith is supported on the feet and there is a gap between the bottomof the catalyst monolith and the bottom surface of the container. Thecarrier outer wall directs the reactant(s) and product upwardly betweenthe inner surface of the carrier outer wall and the outer surface of themonolith catalyst until they reach the underside of the top surface.They are then directed by the underside of the top surface, through theapertures in the carrier outer wall and they then flow downwardlybetween the outer surface of the carrier outer wall and the innersurface of the reactor tube where heat transfer takes place.

In one arrangement, the monolith catalyst has a channel extendinglongitudinally therethrough. Generally the channel will be located onthe central axis of the monolith catalyst. Thus where the reactor tubeis of circular cross-section, the monolith catalyst of this arrangementwill be of annular cross-section. In this arrangement, in use, in avertical reactor with downflow, reactant(s) flow downwardly through thereactor tube and thus first contacts the upper surface of the topsurface of the container and are directed into the channel of themonolith. The reactant(s) then enters the annular monolith catalyst andpasses radially through the catalyst towards the outer surface of thecatalyst monolith. During the passage through the catalyst monolithreaction occurs. Unreacted reactant and product then flow out of themonolith catalyst though the outer surface thereof. The carrier outerwall then directs reactant and product upwardly between the innersurface of the carrier outer wall and the outer surface of the monolithcatalyst until they reach the top surface. They are then directed, bythe underside of the top surface, through the apertures in the carrierouter wall and flow downwardly between the outer surface of the carrierouter wall and the inner surface of the reactor tube where heat transfertakes place.

In the arrangement in which the monolith catalyst includes the channel,the top surface may extend over the monolith catalyst but leave thechannel uncovered. In another arrangement, the top surface may extendacross the channel but will include apertures in this region to allowfor fluid flow.

It will be understood that where the reactor is an upflow reactor or is,for example, in a horizontal orientation, the flow path will differ fromthat described above. However, the principle of the path through thecatalyst carrier will be as described.

Generally, a plurality of catalyst carriers will be stacked within areactor tube. In this arrangement, the reactants/products flowdownwardly between the outer surface of the outer wall of a firstcarrier and the inner surface of the reactor tube until they contact thetop surface and seal of a second catalyst carrier and are directeddownwardly into the second catalyst carrier. The flow path describedabove is then repeated.

The catalyst carrier may be formed of any suitable material. Suchmaterial will generally be selected to withstand the operatingconditions of the reactor. Generally, the catalyst carrier will befabricated from carbon steel, aluminium, stainless steel, other alloysor any material able to withstand the reaction conditions.

The inner container wall and/or the outer container wall can be of anysuitable thickness. Suitable thickness will be of the order of about 0.1mm to about 1.0 mm. In one arrangement it may be of the order of about0.3 mm to about 0.5 mm. The catalyst carrier outer wall may be of ahigher thickness than the walls forming the perforated inner and outercontainer walls when present. As the perforated inner container walland/or the outer container wall where present are not load bearing inthe present invention, they can be made of thinner material than waspossible in the prior art arrangements. This will enable them to be morereadily fabricated and hence cheaper.

In the arrangement where the monolith catalyst has the longitudinalchannel, the surface closing the bottom of the channel and the bottom ofthe container may be formed as a single unit or they may be two separatepieces connected together. The two surfaces may be coplanar but in apreferred arrangement, they are in different planes. In one arrangement,the portion closing the bottom of the channel in the monolith catalystis in a lower plane than the bottom surface of the remainder of thecontainer. This serves to assist in the location of one catalyst carrieronto a catalyst carrier arranged below it when a plurality of containersare to be used. It will be understood that in an alternativearrangement, the surface of the bottom closing the channel in themonolith catalyst may be in a higher plane that the bottom surface ofthe remainder of the container.

In this arrangement, whilst the bottom surface will generally be solid,it may include one or more drain holes. Where one or more drain holesare present, they may be covered by a filter mesh. Similarly a drainhole, optionally covered with a filter mesh, may be present in thesurface closing the bottom of the inner channel. Where the catalystcarrier is to be used in a non-vertical orientation, the drain hole,where present, will be located in an alternative position i.e. one thatis the lowest point in the carrier when in use.

One or more spacer means may extend downwardly from the bottom surfaceof the container. The, or each, spacer means may be formed as separatecomponents or they may be formed by depressions in the bottom surface.Where these spacer means are present they assist in providing a clearpath for the reactants and products flowing between the bottom surfaceof the first catalyst carrier and the top surface of a second lowercatalyst carrier in use. The spacer may be of the order of about 4 mm orabout 5 mm to about 6 mm to about 25 mm deep. Alternatively, oradditionally, spacer means may be present on the top surface or mayextend upwardly from the seal.

The seal or the top surface may include on its upper surface means tolocate the catalyst carrier against a catalyst carrier stacked above thecarrier in use. The means to locate the carrier may be of any suitablearrangement. In one arrangement it comprises one or more upstandingcollars having apertures or spaces therein to allow for the ingress ofreactants. The means may act as baffles to direct the flow.

Whichever arrangement is used for the catalyst carrier, a collar mayextend upwardly from the top surface which in use will locate againstthe under surface of a catalyst carrier stacked above. This collar willgenerally include apertures to allow, in use, flow therethrough. In onearrangement, the collar will be collinear with the carrier outer wall asthis will maximise the strength of the catalyst carrier.

Whichever arrangement is used for the catalyst carrier, the carrierouter wall may be smooth or it may be shaped. If it is shaped, anysuitable shape may be used. Suitable shapes include pleats,corrugations, and the like. The pleats, corrugations and the like willgenerally be arranged longitudinally along the length of the carrier.The shaping of the carrier outer wall increases the surface area of thecarrier outer wall and assists with the insertion of the catalystcarrier into the reactor tube since it will allow any surface roughnesson the inner surface of the reactor tube or differences in tolerances inreactor tubes to be accommodated.

The apertures in the carrier outer wall may be of any configuration.However, their number, size, configuration, and location will beselected to ensure that the flow of the reactant(s) and products is notimpeded while ensuring the carrier outer wall has sufficient materialretained to provide the required strength for load bearing. In onearrangement, the apertures may be holes or slots.

The apertures will be of any suitable size and spacing. The selection ofsuitable sizes will depend on the intrinsic strength of the materialfrom which the catalyst carrier is made, the thickness of material used,the weight and number of catalyst carriers which are to be stacked in areactor tube, the pressure drop noted, the length of the reactor tube,and the like. In one arrangement, the dimensions of the apertures may bedifferent for different catalyst carriers in a reactor tube. Thus in onearrangement, a catalyst carrier to be located, in use, towards the topof a reactor tube may have the region in which the apertures are locatedbe made of up to 90% apertures whereas a catalyst carrier designed to belocated towards the bottom of the reactor tube may have only about 10%of the area as apertures. This is because the catalyst carriers locatedtoward the bottom of a reactor tube will be carrying significantly moreweight than those located at the top. The skilled man will readily beable to calculate the dimensions and shape of the apertures taking intoaccount the amount of wall which is required to be retained to providethe necessary structural integrity and support.

The wall material where the apertures are located in the carrier outerwall may be removed or may be left partially attached to the carrierouter wall. In this arrangement the position of the material can beselected to induce direction for the fluid flow. In one example, theapertures may be slots and the material removed, such as by beingpunched out to form the slots, can be left attached on at least one ofthe four edges of the slot. The material may be angled outwards so thatas the fluid flows out of the catalyst carrier through the slot it isdeflected and a swirl flow pattern is induced in the space between theouter surface of the carrier outer wall and the inner surface of thereactor tube. Swirling the fluid in this way will increase the gasvelocity and further enhance the heat transfer achieved as the fluidflows down the rector tube wall. In one alternative arrangement, theremoved material may be used to strengthen the carrier outer wall wherethe material remains. For example, the removed material may be leftpartially attached and then bent around the attachment to lay on theremaining wall thereby thickening and hence strengthening that sectionof the wall.

Without wishing to be bound by any theory, it is believed that thecarrier outer wall serves to gather the reactants/products from theperforated outer wall of the container or monolith catalyst and directthem towards the top of the catalyst carrier collecting morereactants/products exiting from the outer wall of the container ormonolith catalyst as they move upwardly. As described above,reactants/products are then directed down between the reactor tube walland the outside of the carrier outer wall. By this method the heattransfer is enhanced down the whole length of the catalyst carrier butas the heat exchange is separated from the catalyst, hotter or colder asappropriate heat exchange fluid can be used without quenching thereaction at the reactor tube wall and at the same time ensuring that thetemperature of the catalyst towards the centre of the container isappropriately adjusted.

The seal may be formed in any suitable manner. However, it willgenerally be sufficiently compressible to accommodate the smallestdiameter of the reactor tube. The seal will generally be a flexible,sliding seal. In one arrangement, an O-ring may be used. A compressiblesplit ring or a ring having a high coefficient of expansion could beused. The seal may be formed of any suitable material provided that itcan withstand the reaction conditions. In one arrangement, it may be adeformable flange extending from the carrier outer wall or the topsurface of the catalyst carrier. The flange may be sized to be largerthan the internal diameter of the reactor tube such that as the catalystcarrier is inserted into the reactor tube it is deformed to fit insideand interact with the reactor tube.

Since in the present invention the carrier outer wall is restricted atboth ends by being connected to the base and to the top surface thecarrier outer wall cannot be distorted. This ensures that the catalystcarrier will remain centrally located within the reactor tube with aconstant gap between the carrier outer wall and the inner wall of thereactor tube.

It will be understood that whilst the carrier outer wall is described asextending from the bottom surface to the top surface, the carrier outerwall may continue above the seal. Thus the seal can be located at thetop of the carrier, optionally as part of the top surface, or it may belocated at a suitable point on the carrier outer wall provided that itis located above the apertures in the carrier outer wall. Havingflexibility in where the seal can be located means that the seal can bethicker than in prior arrangements and provide greater contact area withthe reactor tube wall and therefore increase the amount of sealingavailable.

One advantage of the present invention is that catalyst can be providedto the user within the carriers of the present invention which can thenbe readily installed within the reactor tubes with minimum downtime.Thus catalyst may be loaded into the catalyst carrier at the catalystmanufacturing site. It may be pre-reduced and stabilised or encapsulatedobviating the need for catalyst handling on site. Once the catalyst isspent, the carriers can be readily removed from the reactor as discreteunits and readily transported for disposal or regeneration asappropriate.

The apertures in the carrier outer wall can be sealed, for example usingtape, for transportation. This can be important to retain the catalystunder an inert atmosphere or to protect operatives from the catalyst.The seal will then be removed before use. Similarly the top of thecarrier may be sealed.

A further advantage of the present invention is that the problems notedin prior art arrangements in ensuring that each reactor tube of atubular reactor are equally filled are obviated.

The catalyst carrier of the present invention allows catalyst to be usedin medium to highly exothermic or endothermic reactions. The deviceallows the use of large reactor tubes leading to large weight and costreductions for a reactor of a given capacity since heat transfereffectively takes place in a micro-channel zone at the reactor tubewall. This gives excellent heat transfer to or from the cooling/heatingmedium. Furthermore, as the catalyst is separated from thecooling/heating medium, a larger temperature difference can be allowedas the heat exchange effect is separated from the reaction. Where aplurality of catalyst carriers of the present invention is inserted intoa reactor tube this effectively provides a plurality of adiabaticreactors in series in each reactor tube.

The catalyst carrier may be used in a wide range of processes. Examplesof suitable processes include reactors for exothermic reactions such asreactions for the production of methanol, reactions for the productionof ammonia, methanation reactions, shift reactions, oxidation reactionssuch as the formation of maleic anhydride and ethylene oxide,Fischer-Tropsch reactions, and the like. Endothermic reactions such aspre-reforming, dehydrogenation and the like can be carried out inreactors including the catalyst carriers of the present invention.

The catalyst carriers of the present invention may include thetemperature measuring arrangements described in GB1401518.4, thecontents of which are incorporated by reference.

The catalyst carrier of the present invention may be filled or partiallyfilled with any suitable catalyst.

According to a second aspect of the present invention there is provideda reactor tube comprising a plurality of catalyst carriers of theabove-mentioned first aspect of the present invention.

According to a third aspect of the present invention there is provided areactor comprising one or more of the reactor tubes of the above secondaspect.

According to a fourth aspect of the present invention there is provideda process for carrying out a reaction wherein the reactants enter into acatalyst carrier of the above first aspect, a reactor tube of the abovesecond aspect, or a reactor of the above third aspect.

The flow of reactants through the cataylst bed is preferably radial.

The present invention will now be described, by way of example, withreference to the accompanying drawings in which:

FIG. 1 is a perspective view of one embodiment of the catalyst carrierof the present invention;

FIG. 2 is a cross section viewed from the side;

FIG. 3 is a perspective view of one configuration of apertures of thecarrier outer wall;

FIG. 4 is a schematic illustration of the gas flow through theapertures; and

FIG. 5 is a cross section of one alternative arrangement.

One example of a catalyst carrier 1 of the present invention isillustrated in FIGS. 1 to 3. The carrier 1 comprises an annularcontainer 2 which has perforated inner and outer container walls 3, 4.The perforated wall 3 defines an inner channel 5. A top surface 6 closesthe annular container at the top. It is located at a point towards thetop of the inner and outer container walls 3, 4 of the annular container2 such that a lip 7 is formed. A bottom surface 8 closes the bottom ofthe annular container 2 and a surface 9 closes the inner channel 5formed by the inner container wall 3. The surface 9 is located in ahigher plane that that of the bottom surface 8.

A seal 10 extends from the upper surface 6 and an upstanding collar 11is provided coaxial with the inner channel 5.

A cap 12 closes the top of inner channel 5. Apertures 13 in the capallow for fluid ingress.

A carrier outer wall 14 surrounds the container 2. Apertures 16 allowfluid egress from the catalyst carrier.

A catalyst carrier 1 of the present invention is located in a reactortube 15. The flow of gas is illustrated schematically in FIG. 2 by thearrows.

As illustrated in FIG. 3, some of the carrier outer wall material may beleft connected to the carrier outer wall. This flange causes the gas toswirl on its exit from the catalyst carrier as illustrated in FIG. 4.

In the arrangement illustrated in FIG. 5, a spacer 20 may be locatedabove the catalyst carrier, the side walls of the spacer 20 may beintegral with the carrier outer wall or may be a separate item.Apertures 21 are located in the spacer wall to allow flow into the spaceabove the top surface of the catalyst carrier.

In this arrangement, the reactants flow through the apertures 21 in thespacer 20 and into the space above the top surface 6. The flow is thenthe same as illustrated in FIG. 2.

1. A catalyst carrier for insertion in a reactor tube of a tubularreactor, said catalyst carrier comprising: a container for holdingcatalyst in use, said container having a bottom surface closing thecontainer, and a top surface; a carrier outer wall extending from thebottom surface to the top surface; a seal extending from the containerby a distance which extends beyond the carrier outer wall; said carrierouter wall having apertures located below the seal.
 2. A catalystcarrier according to claim 1 comprising: an annular container forholding catalyst in use, said container having a perforated innercontainer wall defining an inner channel, a perforated outer containerwall, a top surface closing the annular container and a bottom surfaceclosing the annular container; a surface closing the bottom of saidinner channel formed by the inner container wall of the annularcontainer.
 3. A catalyst carrier according to claim 2 comprising a capclosing the inner channel formed by the perforated inner container wall,said cap including one or more apertures.
 4. A catalyst carrieraccording to claim 1 wherein the carrier outer wall is smooth or shaped.5. A catalyst carrier according to claim 1 wherein the apertures in thecarrier outer wall are slots.
 6. A catalyst carrier according to claim 1wherein the wall material is left partially attached to the carrier wallwhen the apertures are formed.
 7. A catalyst carrier according to claim6 wherein the attached material is configured to induce direction forthe fluid flow.
 8. A catalyst carrier according to claim 1 additionallyincluding catalyst.
 9. A reactor tube comprising a plurality of catalystcarriers of claim
 1. 10. A reactor including one or more reactor tubesof claim
 9. 11. A process for carrying out a reaction wherein thereactants enter into a catalyst carrier of claim 1.